Tunable narrowband extreme ultraviolet radiation in the range 91–95 nm is produced by sum-frequency mixing of the outputs of a visible pulsed dye amplifier (seeded by a ring dye laser) and of a seeded second-harmonic Nd:YAG laser and subsequent frequency tripling in a gas jet of xenon. The capability of this scheme to provide tunable narrowband extreme ultraviolet radiation is demonstrated in several spectroscopic studies. The bandwidth of this system (0.01 cm-1) is deduced from a recording of absorption spectra of the 4p5(2P1/2) 6d, J=1 line in krypton. The applicability of the system for gas-phase molecular spectroscopic studies is demonstrated in recordings of the Werner bands (4,0) in H2 and (5,0) in D2 at unprecedented absolute accuracy. Line-broadening studies are performed on the b′1Σu+,v=5 valence state in N2, yielding a lifetime of 210±25 ps. A singlet–triplet perturbation, giving rise to an accidental predissociation in an excited 1Π Rydberg state in carbon monoxide at an excitation energy of 107680 cm-1, is analyzed in high resolution.